The transmission of signals in a wireless way (radio) is known in the alarm annunciation art since a long period of time. Fire sensors or detectors, respectively, are also known, which contain a sender for the transmission of signals to a stationary receiver, and vice versa.
From DE 44 08 268 C2 it has become known to store the received field strengths of the radio signals in the receiving apparatus on the occasion of the initial operation of the radio alarm equipment, for the purpose of operation and fail proof security. By doing so, changes in the propagation conditions of the radio waves can be recorded by means of changes of the received field strengths and can be transmitted in the data telegrams. From this, it has become further known to use different frequencies or frequency bands, because the propagation characteristics of radio waves is depending on the carrier frequency used, as is generally known.
In WO 00/43964, a wireless alarm system is described which uses a fire annunciator with a radio sender integrated with it. When a fire is discovered by the fire annunciator, it sends a radio signal. The signal is received by the receiver of a nearest-situated fire extinguisher, a very loud signal sound being given off upon the receipt of the signal, through which the fire extinguisher can be localised.
In JP 200216261 A, a sender module for a fire annunciator is described, which is powered by a battery. The arrangement of the antenna is selected such that it is situated as near as possible to the outer edge of the transmitter module in the fire annunciator, in order to provide an effective emission of the radio waves. In this solution, an optimum circle-shaped emission of the radio waves does not take place, however, because the battery is situated closely to the transmission antenna inside the fire annunciator. As is generally known, the battery is equipped with a metallic jacket, which results in shadowing of the radio waves.
In DE 100 54 297 A1, an electronic fire annunciator is described. A wireless module is hoistable to the fire annunciator from the outside as a separate component. It is advantageous in this that the antenna can be attached to the wireless module on the outside, through which optimum emission characteristics can be obtained. However, it is disadvantageous that a particular module has to be made for the radio transmission, and that a slot with several plug contacts must be provided for the connection to the fire annunciator. By using plug contacts, the safety in operation of such a fire annunciator is impaired.
Upon the emission and the reception of radio signals, several factors influence the coverage of the radio waves or its emission characteristics, respectively. In the most common applications for fire annunciators, batteries or accumulators are integrated in the fire annunciator as power sources. As mentioned already, batteries have metal casings, which are positioned relatively close to the receiving and sending antenna, respectively, in the fire annunciator. Through this, shadowing of the radio waves for certain directions takes place, and from this results a reduced coverage and also, as a result of that, an increased susceptance to trouble for the radio transmission. Arrangement and realisation of the antenna are of great importance. Through these, the maximum distance between receivers and senders for well-performing radio transmission is substantially determined.
The invention is based on the objective to provide an alarm annunciator, particularly a gas or fire annunciator, with a wireless transmitter and/or receiver module in which an optimum wave propagation characteristic is maintained, for the purpose of increasing the safety of operation and of reducing the susceptance of trouble thereof.